Electric furnace.



G. HERING.

ELBCTBIG FURNACE.

Arrmonlon FILED an 2, 1911.

999,720 Patented Aug. 1, 1911.

UNITED STATES PATENT OFFICE.

CARL HERING, 0F PHILADELPHIA, PENNSYLVANIA.

ELECTRIC FURNACE.

To all whom it may concern:

Be it, known that I, CARL Hennvo, a citizen of the United States,residin in the city 0'. Philadelphia, county of P liladelphia, and Stateof Pennsylvania, have invented certain new and useful Improvements inElectric Furnaces, of which the following is a specification.

My invention relates to electric furnaces. and more particularly toelectric furnaces employing electrodes of certain proportions.

My invention resides in an electric furnace comprising improvedelectrodes. for securing minimum electrode loss, in connection withelectric furnace resistors. preferably liquid or molten: and theemployment of my said improved electrodes in combination with anelectric furnace in such arrangement that the power factor of thefurnace is great. when alternating: current is employed.

For an illustration of some forms of application of my invention.reference is to he had to the accompanying drawing, in which:

Figure l is a vertical sectional view of an electric furnace in whichthe resistor is in the form of a column or columns of molten material incombination with my improved electrodes. Fig. 2 is a vertical sectionalVlQW of an electric arc furnace. involving, also resistors incombination with my improved electrodes. Fig. 3 is a side elem tionalView of a metallic or conducting starter.

I. have found that the energy loss in the electrodes of an electricfurnace may be reduced greatly below what has heretofore been commonpractice. 1 have discovered the law of the electrode losses and from itI have found that for a minimum amount of loss' in the electrodes, suchelectrodes must he so proportioned that the (FR loss (heat generated bycurrent in the resistance of the electrodes) shall be equalsubstantially or approximately to twice the heat conduction loss of theelectrodes. By heat conduction loss I mean the loss of heat from theinterior of the furnace through the electrodes by heat conduction whenno current is flowing. I have found that for any other relation betweenthese two losses the co bined loss be- Specification of Letters Patent.Original application filed February 17, 1911, Serial No. 809,123.

Patented Aug. 1, 1911. Divided and this application filed May 2,

Serial No. 624,616.

comes greater. Asa result of roportioning the electrodes so that thisrelation shall hold, the losses of energy in and through the electrodesbecome very small as compared with prior practice. The total loss in theelectrodes will then be equal to the electrical resistance loss only (0R loss) as there will then he no heat lost by conduction. because thetemperature of the hot. end of the electrode willthen be equal to thatof the furnace, and the electrode will therefore he the equivalent of aperfect heat insulator. allowing no heat to pass through it from thefurnace. although the electrode remains a very good electricalconductor. No material is known which has these two qualities co1nhined,namely. heat insulation and electrical conductivity: hut hyproportioning the electrodes according to the laws which I havediscovered. the practical equivalent of these two properties cannevertheless he realized. hile the equations and proportions hereingiven are for electrode materials with ideal properties, such as zeroco-etticicnts for both electric and heat conductivities. theseco-ettieients of actual materials available wary somewhat and.therefore. the results in practice are not exactly those indicated bythe equations and proportions given. but are, for all practicalpurposes. substantially those indicated hy the equations and proportionsgiven. I have found that for each electrode material, this minimum lossis a constant per ampere of current and per degree of furnacetemperature. Also that for a given material this minimum electrode lossis dependent upon the furnace temperature and the current, but not onthe electrode dimensions, except. that the ratio of the length to thecross section of the electrode must he a certain quantity, ashereinafter pointed out. For any given electrode material, temperature,and current, this minimum electrode loss is fixed and cannot be furtherreduced by any change in the dimensions of the electrodc. For differentmaterials I find that. this minimnm-loss is proportional to the squareroot of the ratio of the thermal to the electrical conductivities of theelectrodes. From these laws I find that the minimum loss is generallyleast for the metals, and

that it is very considerably less than for the usual materials carbonand graphite.

It is a part of my invention, therefore, that metal electrodes areemployed, preferably of the same metal as is melted in the furnace, orof metal or material which does not contaminate the material or metalfused in the furnace, and thereby I can greatly reduce the electrodelosses. To obtain this advantage of a lower minimum loss for metalelectrodes they must be proportioned so that the heat conduction loss,with no current flowing, will be equal to half the (PR lossapproximately or substantially. But my improvement is not limited tometal electrodes, for, by observing the novel proortions hereindescribed, carbon and graphite electrodes, giving minimum losses forthose materials, may be employed, and the loss will be found to be muchsmaller than for the carbon and graphite electrodes as heretofore used.I have stated above that this minimum loss is independentof the actualdimensions of the electrodes, that is, they may be lar e or small andyet have the same minimum oss. To get this minimum loss, however, I findthat they must have a certain proportion between their length and theircross section. In order to obtain the best economy of electrodematerial, therefore, the-electrode should be made as short-as possible,as the economy increases inversely as the square of the length. Thecross section is then made to correspond with this length in accordancewith the laws which I have discovered, in order to obtain the minimumloss. From the laws which I have discovered it follows that this economyof material will be greatest, that is, for any given length the crosssection will be least, when the square root of the product of theelectrical and the thermal conductivities is greatest. Hence, I findthat as far as economy of material is concerned, those matcrialsare bestin which this product is greatest. In any given material, therefore, thedesirable qualitiesare, to a certain ektent, opposed, with respect toeconomy of power as compared with economy of material. I have discoveredthat if K and ll: represent the electrical and thermal conductivities ofthe material,'then the minimum power loss in them, in the form of theheat which leaves them at the outside terminals, is least when K dividedby k is greatest. On

. the other hand, the economy of material is best when the product of kand K is greatest; It is, therefore, the quotient and the prodiict ofthe electrical and thermal conductivities which determine theirsuitability for which must be compared and not the quo tients andproducts irectly. From the conductivities of different materials as faras they are known, I find, from the law which I have discovered, thatthe square root' of these quotients and products are as a rule greatestfor the metals. as distinguished from the usual electrode1naterials,carbon and graphite. The difference is great. Hence, I have found itmuch more economical to use metal electrodes Whenever possible.

\Vhen metal electrodes are used and proportioned in accordance with thelaws which I have discovered, they will remain solid at the externalends although they will be at the temperature of fusion at the inside orfurnace ends. The reason is that when so proportioned there will be noheat conducted by the electrodes from the interior of the furnace, andall the heat generated in them by the current will be led off at thecool or outside end just asfast as it is generated in it; hence theirtemperature will not increase and they will remain unfused except attheir extreme inside ends. lf continuously covered with fused metal attheir inside or hot ends they will not be consumed and if made of thesame metal as that fused in the furnace, or of one which is nonmisciblcwith the fused material, they will not contaminate the latter. Thisstate, as I have found, is also the state of least total loss in theelectrodes.

. From the laws above stated I have deduced the following formula:

X 2.8940 {MT in which X is the total minimum loss in watts in or throughthe clectrodrs. 2.894: is a constant involving no physical properties, Cis the current in amperes, is is the heat conductivity in gram caloriesper second, cubic inch units, 7 the electrical resistivity in ohms,cubic inch units, and T the temperature difference between the insideand outside ends of the elcctr'ode in centigrade dcgrccs. And I havededuced the followin formula for determining, the condition 0 properproportions of the electrodes for minimum loss:

r lcT in which S is the cross section of the electrodes in squareinches, L their length in inches, the current in amperes, r, In and Tbeing the same as above. The electrodes must have this proportion inorder to obtain the minimum loss given in the first formula.

Then the thermal conductivity is in the above formulae is expressed inwatts in place of in calories per second, the numerical constants inthese formulae, namely, 2.894 and 0.3456, disappear, and a factor 2accomsection to the length 0 panics the factor It, so that theseformulae take the form, respectively, as follows:

ives the ratio of the the electrodes and therefore leaves a choice ofeither, but not of both. The length should be made as short as possible;it is usually determined by the general design and thickness of thefurnace walls or other considerations. The quantity of electrodematerial increases as the square of the length. It follows, therefore,that in accordance with my discoveries and invention, I may greatlyreduce the size of, and therefore cheapen, the electrodes heretoforeused in the art and at the same time secure a minimum loss of energy inthe electrodes, thus leavin greater amounts of energy for useful woriwithin the furnace and, in consequence, increasingthe efliciency of thefurnace. V I

If by the electrode elliciency is meant the ratio of the energy set free1n the interior of the furnace, that is, between the hot ends of the twoelectrodes, divided b the total energy between the two cold on s, thenfor a iven minimum loss in the electrodes, this eth ciency willevidently be higher the greater between the hot ends, as e drop ofvoltage in one e electrodes. By my invention the latter may be made verysmall, much smaller than heretofore, hence for a given current andvoltage of a furnace there will be more useful heat generated in thefurnace. But to increase this efficiency still more the dro of voltagebetween the two hot ends should To do this with a liqui resistor mayrequire this resister to be made long and small in section, hence I mayin those cases refer to use the are as this has a relative y high dropof potential in a small space. Or still-better may use several arcs inseries.

In Fig. 1 is shown an electric furnace in vertical section having ahearth. A; this hearth may ta e an suitable or desired form, as the heatpro ucing resistor'is practical] independent of the proportions of thisiearth or the amount iof molten material in it. Upon the hearth A is amass B, of molten iron or other-material under treatment, the moltenmaterial extendin also downwardly into the columns C and I), the moltenmaterial in these columns making electrical end-on contactwith thefurnace electrodes .E, E, roportioned and constructed as hereinbe oredescribed, which extend through the bottom or wall.of the furnace, andmay terminate outside in conduct- This second formula the drop of voltacom ared with t f th be made as rest as possible.

iempltiyed. The dividing member S 1n co led, if desired, by a waterjacket. The furnace extends upwardly in the form of a dome G, preferablyenlarging toward the bottom, such dome being lpreferably filled with thecharging n'lateria H, as iron ore or other material, which may beintroduced through the opening I at the top, which is thereby preheated.

The furnace may be started by a charge of molten material or by acasting of preferably the same materia as that to be treated, extendingdownwardly in the columns C and D into contact with the electrodes E, E,such casting bein continuous and bridging the columns C- an D at thetop. When the current is turned on, it flows from one electrode throughone of the columns and out through the other column and other electrode,the casting, when such is employed for starting, becoming hotter andhotter until finally melted.

M is.a tap hole communicating with the column C for drawing oil thefinished material, and a similar tap hole N may be provided forcommunicating with he other column D for the same purpose, if desired.Or the ta hole may communicate with the bottom of lzhe hearth, ifdesired, or tap holes ma be placed at both places.

Ill operation, a minimum amount of energy is lost in the electrodes I),E, and the heat is produced by the current in the columns C and D, themolten masses in these columns constituting the resistor.

In Fig. 2, I have shown an arc furnace having the electrodes E, E,proportioned as herein described, which may be metallic, communicatingwith the separated baths B and B of moltenmaterial, a dividing wall ormember S being provided. The are may be started by a bridge piece m,such as shown in Fig. 3, made of the same metal as that in the baths Band B, by placing the same over the dividing memer S; the member thenmelts and an arc ois formed between the two baths B and- Or the are maybe started by granular oonducti material extending over the member intocontact with the two baths, or the baths may be agitated to comemomentarily into contact with each other above the member S, or anyother means may be may be kept om fusing by a circulatlonof water orother cooling material through the-opening or tubeT. Or the magneticblow-out principle may be used to kee the arcs far-- ther from thedividing mcm er S.

In both the forms of furnaces herein shown, it will be noticed that thetwo terminals' or electrodes may be brought out. close together, becauseof their small size, due to my invention,.thereby facilitating theenlargements, F, F, which may be 66 connections to the transformer andthus increasing the power factor, when alternating current 15 used,since the area inclosed by the conducting 100 formed within the furnaceis reatl re uced.-

The e ectro es are not consumed and therefore do not contaminate thefused product and do not have to be advanced into the furnace. Inconsequence, the construction of the furnace is greatly sim lifted andcheapcned. Unless proportionc as I have shown, the losses through metalelectrodes may become very large, due to their high heat conductivity.

By constructing a furnace electrode as herembefore described, theelectrode section selves, proportioned, as herein described, for iminimum loss, but claim said electrodes herein only in combination withother features; the electrodes themselves, roportioned for minimum loss,are claims in the above-mentioned application Serial No. 009,123.

What I claim is: '1. In an electric furnace, molten conduct ing matelialserving as a furnace resistor,

and an electrode in electrical commnnication with said resistor forcommunicating heating current to said resistoiy-the length and crosssection of said electrode being so related that the resistor heatingcurrent passed through said electrode raises said electrode to atemperature preventing heat conduction through said electrode from saidmolten material. i

2'. In an electric furnace,a resistor, a plurality of electrodeselectrically communicatin withsaid resistor, and an insulating 'divi ingwall between said electrodes, said electrodes; pro ortioned" for minimumelectrode lose an ntially as described, whereby the distance betweensaid electrodes is small and the area. inclosed by the furnace circuitis small and the power factor great when alternating current is passedthrough said electrodes.

3. In an electric furnace, axesistor, and an electrode for communicatingheating current to said resistor, said electrode being soproportioned-that the CPR heat developed in said electrode by theresistor heating current passed through said electrode raises posed inend on contact with said mass of molten metal, said metal electrodehaving is resistance such that the CR heat developed therein by currenttransmitted therethrough to said mass shall be substantially equal totwice the heat conduction loss when no current flows.

5 In an electric furnace, an insulating dividing wall, columnsofconductin material on opposite sides of said wall, an electrodes onopposite sides of said wall electrically communicating with saidconducting columns, saidclectrodes proportioned for minimum electrodelosses substantially as described, whereby the distance between saidelectrodes is small and the area of the furnace circuit is small and thepower factor great when alternating current is passed through aidelectrodes.

6'. In an electric furnace, a. dividing wall within said, furnace.containers for molten material on opposite sides of said dividing wallwithin the furnace wall, electrodes proportioncd for minimumelectrcde'losses sub,-

fillllli t lh. as herein described extending through tilt. furnace walland disposed in oml on cont-act with said separate masses on either sideof said dividing wall, said masses being adapted to be connected b anare extending over said dividing we. 1.

7. In an electric furnace, a container for a mass of molten metal, ametal electrode extending through the furnace wall in electricalcommunication with said mass, the:

cross section of said'clectrode so related to the length of saidelectrode that the CR heat developed in said electrode by currenttransmitted t-herethrough to said mass raises said electrode to atemperature preventing heat conduction through said electrode from saidmass.

8. In an electric furnace, a molten-resistor, an electrode in end-0ncontact therewith for communicating heating current to acid resister,said electrode having such resistance that the (FR heat developed insaid electrode by said resistor heating current raises the end of saidelectrode in contact with said resistor to a temperature substantiallyequal to the temperature of said resistor.

9'. In an electric furnace, the combination with a container formaterial to-Ue treated within the furnace wall, of an electrode ex- Itending throughsaid walhand disposed in electrical commui'iicat-lonwith'sald mater al,- the cross sect-ion"'of said electrode being sosmall that the C'R heat developed in said electrode by current passedtherethough to said material raises said electrode to a temperaturepreventing heat conduction through said electrode from said materialwithin said furnace.

10. In an electric furnace, the combination with a container formaterial to be treated within the furnace wall, of an electrodeextending through said wall and disposed in clectrlcnl communicationwith said nmterial, the cross section of said electrode being uniformand so small that the (PR heat developed in said electrode by currentpassed therethrough to said material raises said electrode to atemperature preventing heat conduction outwardly through said electrode.

In testimony whereof I have hereunto afiixed my'signature in thepresence of the two subscribing witnesses.

CA RL H ERI NG.

